Ignition device



July 2, 1940. c. R. BENTON 2,206,073

IGNITION DEVICE Filed Oct. 28. 1937 f'Q ma wk l6 s .p""- r 26' if 42' r M ll hp/ 2 F Z4 E- E 1 Z2 M /Z 2 f 11v VENTOR CsazZ 72' ,Belzzozz. B Y

ATTORNEY Patented July 2, 1940 UNITED STATES PATENT OFFICE 5 Claims.

This invention relates to igniters and more particularly to spark plugs especially adapted to withstand severe operating conditions.

Spark plugs for such uses must withstand high temperatures and pressures, and their insulation must be able to resist the high voltage necessary to produce a satisfactory spark under these conditions. In addition, the plugs must withstand severe vibration and large temperature changes which further increase the difficulty of providing plugs that will operate satisfactorily for a reasonable length of time.

Plugs for such purposes have been developed in which mica is used as the insulating medium.

i Many of such plugs wrap the central spark .plug electrode in a mica sheet, this forming the electrical insulation. Surrounding the spirally wrapped mica may be placed layers of mica resembling a stack of washers, these forming a mechanical protection for the electrical insulating tube formed by the spiral layers of the mica sheet.

It has heretofore been difficult for the manufacturer to wrap the mica sufiiciently tightly to form a gas-tight seal. Another difficulty is the 5 avoidance of air spaces between the mica washers ancl the mica tube. These spaces are objectionable because they become filled with ionized gases which form a path for leakage electric current. Many attempts to compress the mica tube 3 have resulted in rupturing the sheet from which it is formed. To prevent gas pockets attempts have been made to fill them beforehand with materials which will not ionize.

Both these objections are not completely solved by the remedies which have heretofore beentried and it is therefore one of the principal objects of this invention to provide a spark plug which will not be subject to the abovementioned causes of deterioration. More specifically, it is an object of the present invention to provide a.

spark plug in which the mica tube surrounding the central electrode is tightly compressed'over a substantial portion of its length and in which the mica washers have a tight fit on the mica tube which passes through them. 7

Another object of this invention is to provide a method of assembling a spark plug so that the layers of the mica tube are placed under ex-- m Fig. 2 is a cross-section taken on the line drawing which illustrates the preferred embodi- 2-2 of Fig. 1 and looking in the direction of the arrows.

Fig. 3 is a cross-section taken on the line 2-3 of Fig. 1 and looking in the direction of the arrows. I

Fig.4 is an end view looking up at the bottom of the'spark plug.

The particular embodiment of the inventio shown in the drawing comprises a shell Ill externally threaded at its lower end II, as is common practice, and having a collar I2 to receive a gasket and a hexagonal portion I3 to receive a wrench. A nut or bushing ll having an integral tubular extension I5 is screwed into the top 'of bore N5 of the shell ill, the tubular extension serving as a radio shield. The nut I4 presses down on a collar IS on a gland 20, forcing the tapered lower end of the gland down into the tapered lower position of the bore in the shell l0 and producing a gas-tight joint between the gland and the shell.

The gland 20 surrounds a central electrode 2|, made of steel or other equivalent material, the mica which forms its insulation. The stem of the electrode 2| is cylindrical and is surrounded by a tapered sleeve 22, the larger end of the sleeve being at'the lower end of the electrode. The sleeve 22 is? .preferably made of a material softer than that forming the electrode 2| such as brass, and is surrounded by a spirally tapered tube of mica 23 formed of one or more sheets wrapped several times around the electrode. The electrode 2| and the sleeve 22 cooperate to form a conducting path.

The electrode 2|, the brasssleeve 22, and the mica tube 23 fittightly in a tapered hole extending through the bushing or gland 20 and also project some distance above and'below.' The portions of the tube projecting from the gland are enclosed in two stacks of mica washers 24 and 25. The mica washers 24 around the upper part of the tube are clamped vertically between the top of the gland 2| and a metal washer 26, the upper end of theelectrode 2| being flanged or spun over to hold the parts together. The mica washers 25 around the lower part of the tube are similarly clamped between the lower part of the gland 20 and a head 29 on the electrode, and, in addition, the upper part of this group of washers fits into a counterbore in the bottom of the gland 20 and are surrounded by a skirt 30 forming the wallet the counter- The head 28 of the center electrode 2| is provided with a'tip 22 brazed or. welded on and made of an alloy which is especially resistant to the eroding effect of electric sparks. A second elec-' trode 33, made of thesame alloy, extends across and is brazed or'welded to, the lower end of the shell ll under the center electrode trip 32 and at the proper distance from it to provide the best spark. The spark plug is assem led bytightly winding several layers of thin sheet mica onto a tapered arbor or mandrel to form the tube 23. The lower mica washers 25,.the bores of which have been taper reamed, are slid over the tube which is then pushed through the gland til-and through the. upper mica washers 2%. As the mandrel and tube are pushed home by hand, a movement of the difierent layers oi the tube relative to each other occurs. This movement consists of a slight longitudinal sliding of each layer, and a simultaneous unwinding of the tube soc that its initial tight fit is maintained.

The friction between the mandrel and the mner layer of the tube, and that between the outer layer "of the tube and the gland causes the longitudinal sliding of the layers relative to each 29 other, and, once-the static friction has been overand the brass sleeve 22 is pushed into its place,

but, while the mandrel was pushed in by hand, the brass sleeve is forced in by a press. It has been found that, in assembling a spark plug of means for forming a gas-tight electrically insulated seal between said electrode and said shell,

' said means including a tube formed of layers of conventional size, a pressure of a thousand pounds on the end of the sleeve produces excellent results. This great pressure forces the brass sleeve in further than the mandrel went and causes 5 more motion of the layers oi mica. 'As a result of this final movement and the wedging action of the tapered sleeve, the mica is under great radial pressure without being under excessive circumferential tension, and the space between the 4( layers-of the tube and between the, tube and the mica washers 24 and 25 is thus made gas tight. The electrode 2! is then forced. into place, ex-

pending the brass sleeve 22 slightly or, if the sleeve was compressed near its inner end by the 5 wedging action on its sides as it, was forced in,

re-expanding it to its original size. This expansion or re-expansion of the brass. sleeve is slight, but it places the mica tube under such extreme pressure that it remains tightand proof combustion-even after the plug has repeatedly been heated up to extreme operating temperatures and cooled down again to atmospheric temperatures. e expansion of the brass sleeve 22 mica washers 24 and 25 so that no space is left into whlch destructive gases or particles'mlghtfind their way.

. 'Wliile I have-herein described in some detail 66 a specific embodiment of my invention, which 65 that changes may be made therein without departing from the spirit or scope of my invention. I claim? 1. In a spark'pl ug, an electrode and a sleeve' combining to form a conductor having atapered terial between said conductor and bushing some of said layers .lylng substantially parallel to the against infiltration of gas or other products of also forces the tube 23 to fit tightly inside of the exterior, a bushing, and layers of insulating mainsulating material wrapped .cylindrically about said electrode, a staclr of washers of insulating material surrounding said tube for only a portion of the length thereof, and a hollow sleeve between said electrode and saidtube, said sleeve bearing against said shoulder and having a tapered exterior extending throughout substantially the full interior length of said stack and tube,'said sleeve being made of amaterial suificiently ductile to conform to irregularities on the inner surface of said tube and expand said tube radially outwardly without deforming the individual layers forming said tube, thereby closing the gap between said stack and'said tube and also. the gap between said tube and said shell.

3. In a spark plug, a shell, 9, central electrode mounted therein and having a shoulder, and means for forming a gas-tight electrically insulated seal between said electrode and said shell, said means including a tube formed of layers of insulating material wrapped cylindrlcally about said electrode, a stack of washers of insulating materialsurrounding said tube for only a portion of the length thereof, and a tapered hollow sleeve between said electrode and said tube and bearing against said shoulder, whereby when said shoulder is pressed axially of said tube, the tapered exterior of said sleeve will radially expand said tube andsaid shoulder will axially compress said stack against said shell.

4. In, a spark plug, an outer body having an electrode affixed thereto, an inner electrode assemblyremovably mounted in said body, said assembly comprising a central electrode having a shoulder adjacent each end thereof, a supporting shell "surrounding the mid-portion of said, electrode, a tube formed of layers of insulating material lying in contact with the inner surface of said shell, said tube extending substantially the. full distance between said shoulders, a stack of annnular layers of insulating material surrounding and in contact with said tube and extending between each end of the supporting shell and the shoulders on said central electrode, and a hollow sleeve surrounding said central electrode and extending throughout substantiallythe full length of said tube, said sleeve' having an exterior tapered surface throughout substantially its full length whereby to expand said tube into gas-tight contact with said stacks and said shell.

5. In an igniter, an electrode having a stem, a sleeve on said stem formed of a metal softer than said stem and having anexteriorly tapered portion, insulating material including layers of insulating material perpendicular to said stem and surrounding at leastthe lower portionoi said tapered portion, and a retaining member surrounding said insulating material and extending above said perpendicularly arranged layers.

oncm R. BENTON. 

